As Vito Ricci has already pointed out, the Welsh test is for two group unpaired data with unequal variance assumption.
If you have the original data, say x and y, then you can simply do t.test( x, y, paired=FALSE, var.equal=FALSE ). If you do not have the original data, you can still calculate the relevant statistics and p-value as long as you know the group length and variance. 'stats:::t.test.default' shows you the code behind t-test. I think the relevant bits are as follows mx <- 0 my <- 2 mu <- 0 # You will need to fill these with your observed values vy <- var(y) vx <- var(x) ny <- length(y) ny <- length(y) stderrx <- sqrt(vx/nx) stderry <- sqrt(vy/ny) stderr <- sqrt(stderrx^2 + stderry^2) df <- stderr^4/(stderrx^4/(nx - 1) + stderry^4/(ny - 1)) tstat <- (mx - my - mu)/stderr # for two sided alternative pval <- 2 * pt(-abs(tstat), df) alpha <- 1 - conf.level cint <- qt(1 - alpha/2, df) cint <- tstat + c(-cint, cint) cint <- mu + cint * stderr On Wed, 2004-11-24 at 04:28, Steve Freeman wrote: > Hi. > > I'd like to do a t-test to compare the Delta values of items with Crit=1 > with Delta values of items with Crit=0. What is the t.test syntax? > > It should produce a result like this below (I can't get in touch with the > person who originally did this for me) > > Welch Two Sample t-test > > data: t1$Delta by Crit > t = -3.4105, df = 8.674, p-value = 0.008173 alternative hypothesis: true > difference in means is not equal to 0 > 95 percent confidence interval: > -0.04506155 -0.00899827 > sample estimates: > mean in group FALSE mean in group TRUE > 0.03331391 0.06034382 > > Thanks. > > ------------------------------------ > Steven F. Freeman * Center for Organizational Dynamics * University of > Pennsylvania * (215) 898-6967 * Fax: (215) 898-8934 * Cell: (215) 802-4680 * > [EMAIL PROTECTED] * http://center.grad.upenn.edu/faculty/freeman.html > > > [[alternative HTML version deleted]] > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html -- Adaikalavan Ramasamy [EMAIL PROTECTED] Centre for Statistics in Medicine http://www.ihs.ox.ac.uk/csm/ Cancer Research UK Tel : 01865 226 677 Old Road Campus, Headington, Oxford Fax : 01865 226 962 ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
